Soil conditioning agglomerates containing calcium

ABSTRACT

Mechanically strong, water-disintegrable agglomerates for use as a soil conditioner produced from cement kiln dust and other particulate calcium sources containing CaO or Ca(OH) 2  and other calcium-containing compounds having the potential to be hydrated and a process for forming such agglomerates are disclosed. The process comprises combining the particulate calcium source and a water-soluble binder to produce agglomerates which are then subjected to controlled drying such that the dried agglomerates having a size ranging from −7 to +8 Tyler Standard Sieve Series exhibit an average green crush strength of at least about 2 pounds (about 0.9 kg).

This application is a continuation of U.S. patent application Ser. No.09/067,283, filed Apr. 27, 1998, pending which is a continuation-in-partof U.S. patent application Ser. No. 08/672,226, filed Jul. 5, 1996, nowU.S. Pat. No. 5,743,934, which is a continuation-in-part of U.S. patentapplication Ser. No. 08/398,657, filed Mar. 3, 1995, now abandoned, thedisclosures of which are expressly incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to mechanically strong,water-disintegrable agglomerates containing various particulate calciumsources for use as a soil conditioner to neutralize soil acidity andprovide a source of nutrient values. The present invention also relatesto processes for forming such agglomerates.

Soil conditioners or liming agents are widely used in agriculture, lawncare and gardening to reduce soil acidity and promote plant health. Avariety of calcium-containing materials, in particulate or granulatedform, are used as soil liming agents. Conventional liming agentsinclude: limestone (CaCO₃), dolomitic limestone (CaOMgO.2CO₂), lime(CaO), slaked or hydrated lime (Ca(OH)₂), and gypsum (CaSO₄.2H₂O).

Many industrial processes produce waste solids containing calcium. Forexample, the manufacture of cement and lime is accompanied by thegeneration of large quantities of dust collected from the hot gaseouseffluents vented from the kiln. Similar calcium-containing dusts arerecovered from the stack gases and ash residues produced during theburning of manure fuels (i.e., manure ash). These particulate wastesshare two properties that make them potentially useful for applicationto cultivated soils: (1) significant acid neutralization capacity; and(2) high concentrations of calcium and other important soil nutrientssuch as potassium and sulfur.

Although some have suggested liming soils with cement kiln dust (See T.A. Davis, et al., “Disposal and Utilization of Waste Kiln Dust FromCement Industry”, EPA Report No. 670/2-75-043 (May 1975)) as a way ofreclaiming this sizeable waste stream, one serious hindrance to expandedagricultural use cement kiln dust and similar waste products are theproblems associated with storage, handling and application of thesefinely divided materials to soils.

Raw cement kiln dust, for example, is extremely fine, typicallyconsisting of particles having an average particle size much less than100 μm, with a large portion of particles often having a particle sizeof 10 μm or less. As a result, the dust is easily carried away by thewind and is difficult to bulk-blend with other materials in preparingvarious fertilizer formulations. Furthermore, modern fertilizerapplication equipment for broadcast or row placement of solidfertilizers, is designed for handling free-flowing, granular orpelletized materials having an appreciable mean diameter, not dust.Consequently, numerous problems are encountered when such equipment isemployed for field application of finely-divided dust.

Accordingly, it would be highly beneficial to develop a process forgranulating or agglomerating cement kiln dust and othercalcium-containing materials capable of consistently producing amechanically strong soil conditioning agglomerate that readilydisintegrates when contacted with water.

SUMMARY OF THE INVENTION

Among the objects of the present invention, therefore, are the provisionof a process for forming an agglomerate comprising calcium-containingwaste materials such as cement kiln dust for use as a soil conditioningagent; the provision of such a process capable of producing anagglomerate having sufficient mechanical strength to withstand therigors of handling, transport and application without excessive dusting;and the provision of such a process which produces an agglomerate whichdisintegrates readily into particles having substantially the same sizeas the raw materials used to form the agglomerate once the agglomerateis incorporated into soil and exposed to water so that the variousbeneficial components of the agglomerate may be rapidly utilized by thesoil.

Briefly, therefore, the present invention is directed to a process forforming an agglomerate for use as a soil conditioning agent. The processcomprises preparing a preagglomerate containing a water-soluble binderand a particulate calcium source comprising CaO or Ca(OH)₂. The combinedconcentration of CaO and other calcium-containing compounds having thepotential to be hydrated in the preagglomerate is no greater than about10% by weight. The preagglomerate is pelletized to form the agglomerate.The proportion of the particulate calcium source in the preagglomerateis sufficient such that the agglomerate contains at least about 15% byweight of the particulate calcium source. Once formed, the agglomerateis dried. Drying of the agglomerate is controlled such that driedagglomerates having a size ranging from −7 to +8 Tyler Standard SieveSeries exhibit an average green crush strength of at least about 2pounds.

In another embodiment, the process for forming an agglomerate for use asa soil conditioning agent comprises preparing a preagglomeratecontaining a water-soluble binder and a particulate calcium sourcecomprising CaO or Ca(OH)₂ combined with at least one othercalcium-containing secondary plant nutrient source selected from thegroup consisting of limestone, dolomitic limestone, gypsum, lime,hydrated lime and mixtures thereof. The particulate calcium source has aparticle size distribution such that less than about 1% by weight of theparticulate calcium source is +20 mesh and less than about 10% by weightof the particulate calcium source is −20 +100 mesh Tyler Standard SieveSeries. The combined concentration of CaO and other calcium-containingcompounds having the potential to be hydrated in the preagglomerate isno greater than about 10% by weight. The preagglomerate is pelletized toform the agglomerate. Once formed, the agglomerate is dried in acontrolled fashion such that dried agglomerates having a size rangingfrom −7 to +8 Tyler Standard Sieve Series exhibit an average green crushstrength of at least about 2 pounds.

The present invention is further directed to an agglomerate for use as asoil conditioner. The agglomerate is formed by pelletizing apreagglomerate containing a water-soluble binder and a particulatecalcium source comprising CaO or Ca(OH)₂ combined with at least oneother calcium-containing secondary plant nutrient source selected fromthe group consisting of limestone, dolomitic limestone, gypsum, lime,hydrated lime and mixtures thereof. The combined concentration of CaOand other calcium-containing compounds having the potential to behydrated in the preagglomerate from which the agglomerate is formed isno greater than about 10% by weight. Furthermore, the particulatecalcium source has a particle size distribution such that less thanabout 1% by weight of the particulate calcium source is +20 mesh andless than about 10% by weight of the particulate calcium source is −20+100 mesh Tyler Standard Sieve Series.

In another embodiment, the agglomerate for use as a soil conditioner isformed by pelletizing a preagglomerate containing a water-solublebinder, a primary plant nutrient source providing a source of availablenitrogen and a particulate calcium source comprising CaO or Ca(OH)₂. Theproportions of the primary plant nutrient source and the particulatecalcium source in the preagglomerate are sufficient such that theagglomerate comprises about 15% to about 60% by weight of theparticulate calcium source and about 30% to about 80% by weight of theprimary plant nutrient source. The combined concentration of CaO andother calcium-containing compounds having the potential to be hydratedin the preagglomerate from which the agglomerate is formed is no greaterthan about 10% by weight. Furthermore, the agglomerate exhibits anaverage green crush strength of at least about 2 pounds when sizedranging from −7 to +8 Tyler Standard Sieve Series.

In a still further embodiment, the agglomerate for use as a soilconditioner is formed by pelletizing a preagglomerate containing awater-soluble binder, a primary plant nutrient source providing a sourceof potassium and a particulate calcium source comprising CaO or Ca(OH)₂.The proportions of the primary plant nutrient source and the particulatecalcium source in the preagglomerate are sufficient such that theagglomerate comprises about 15% to about 60% by weight of theparticulate calcium source and about 30% to about 80% by weight of theprimary plant nutrient source. The combined concentration of CaO andother calcium-containing compounds having the potential to be hydratedin the preagglomerate from which the agglomerate is formed is no greaterthan about 10% by weight. Furthermore, the agglomerate exhibits anaverage green crush strength of at least about 2 pounds when sizedranging from −7 to +8 Tyler Standard Sieve Series.

Other objects and features of this invention will be in part apparentand in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a flow diagram of one embodiment of the process of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, mechanically-strong,water-disintegrable agglomerates produced from various particulatecalcium sources including calcium-containing waste materials as well asconventional soil liming agents are provided. The agglomerates areuseful as soil conditioners to neutralize soil acidity and provide asource of nutrient values. Processes for forming the agglomerates arealso provided. As used herein, agglomerate means pellets andirregularly-shaped particles formed by the consolidation of smallerparticles. All mesh sizes herein are in reference to the Tyler StandardSieve Series.

The agglomerates of the present invention are made by pelletizing apreagglomerate mixture prepared by combining a water-soluble binder witha particulate calcium source as described in detail below.

The particulate calcium source may comprise cement kiln dust, lime kilndust, manure ash or other calcium-containing secondary plant nutrientsources including conventional liming agents such as limestone,dolomitic limestone, gypsum, lime and hydrated lime. The gypsum may bederived from natural sources as well as from byproducts of chemicaloperations such as the wet solids and slurries produced in limescrubbing stack gases to remove sulfur dioxide. In general, theagglomerates contain at least about 15% by weight of the particulatecalcium source.

The particulate calcium source may consist essentially of any one of theaforementioned calcium-containing materials as well as mixtures thereofand should be selected so as to have a relatively high calcium carbonateequivalent value. Preferably, the particulate calcium source has acalcium carbonate equivalent value in excess of 85%, more preferably inexcess of about 90%, and most preferably in excess of about 92.5%. Ifcement kiln dust, lime kiln dust, manure ash or other calcium-containingwaste materials are combined with another calcium-containing secondaryplant nutrient source, it is preferred that the other calcium sourcesconstitute no more than about 80% by weight of the particulate calciumsource, more preferably from about 30% to about 70% by weight of theparticulate calcium source.

In order to achieve the mechanical strength and disintegrationcharacteristics desired in the agglomerate, the amount of water-solublebinder present in the preagglomerate is generally at least about 1% byweight (dry basis). Use of larger quantities of binder generally yieldshigher strength agglomerates which may be desirable in someapplications. Preferably, the amount of binder present in thepreagglomerate is at least about 2%, more preferably, at least about 4%by weight (dry basis). Preferably, the amount of binder present in thepreagglomerate is between about 4% and about 25% by weight (dry basis).

Suitable water-soluble binders for use in the present invention includelignosulfonates, lignosulfonate salts (e.g., calcium lignosulfonate,ammonium lignosulfonate), water-soluble fertilizer materials (e.g.,potash, ammonium nitrate, urea, diammonium phosphate), synthetic ornaturally occurring polymers (e.g., polyvinyl alcohol, polyacrylic acidsalts, amylose, methylcellulose, hydroxyethylcellulose,carboxymethylcellulose, ethylhydroxyethylcellulose, corr starch andwheat starch) and sugar-based binders such as molasses and those sold byRDE, Inc., Crystal Lake, Ill., 60014 under the “BREWEX” and “MOLTECH”trademarks, as well as mixtures of these various materials. Among thepreferred binders for use in the present invention are the liquid blendsof granulating agents and surfactants sold by Arr-Maz Products, WinterHaven, Fla. 33880, under the product designations KGA-300 and KGA-250.An especially preferred binder is the calcium salt of lignosulfonatesuch as that sold by LignoTech USA, Greenwich, Conn. 06830, under thetrademark “NORLIG A”.

In addition to the particulate calcium source and water-soluble binder,the agglomerates may contain appreciable amounts of various particulateadditives. For example, the agglomerates may comprise a primary plantnutrient source (i.e., a source of nitrogen, phosphorous and/orpotassium), a secondary plant nutrient source (i.e., a source ofmagnesium, sulfur, and/or calcium), and/or a micronutrient source (e.g.,a source of iron, copper, boron, selenium, chromium, vanadium,manganese, zinc and/or molybdenum). Upon disintegration of theagglomerate, these additives deliver their benefit to the soil alongwith the particulate calcium source.

For some applications, the agglomerate may contain only a particulatecalcium source and a water-soluble binder, whereas in other applicationsthe particulate calcium source will account for from about 15% to about50% of the weight of the agglomerate. In some instances, it will bedesirable to include appreciable quantities of a primary plant nutrientsource of the type typically used in N-P-K fertilizer formulations inthe agglomerate. For example, the agglomerate may contain conventionalsources of nitrogen, phosphorous and potassium such as ammonium nitrate,ammonium sulfate, alkali metal nitrates, urea, rock phosphate, ammoniumphosphate (e.g., (NH₄)₂HPO₄, NH₄H₂PO₄.H₃PO₄ and NH₄H₂PO₄) bone mealslag, aluminum phosphate, superphosphate, potash, and potassium salts(e.g., chlorides, sulfates and nitrates) and mixtures thereof. Theagglomerate may also contain organic fertilizer ingredients such asmanure and residues from sewage treatment plants. For such applications,it is preferred that the agglomerate contain from about 5% to about 40%available nitrogen, more preferably from about 8% to about 15% availablenitrogen, about 10% to about 50% available phosphoric acid, and/or about10% to about 50% available potash. If urea, potash or other N-P-Kfertilizer ingredient is used as a binder, this also has the furtherbeneficial effect of increasing the primary plant nutrient content ofthe agglomerate. Furthermore, if desired, the agglomerates mayadditionally include a micronutrient source.

A preferred agglomerate for use as a nitrogen source contains about 30%to about 80%, more preferably about 55% to about 60% by weight, urea orother source of available nitrogen (e.g., ammonium nitrate) and at leastabout 15% to about 60%, more preferably about 35% to about 45% by weightof the particulate calcium source, based upon the weight of theagglomerate. In accordance with another preferred embodiment, anagglomerate for use as a potassium source contains about 30% to about80%, more preferably about 45% to about 55% by weight, potassiumchloride, potash or other source of potassium and at least about 15% toabout 60%, more preferably about 45% to about 50% by weight of a calciumsource, based upon the weight of the agglomerate. In these formulations,the N-P-K fertilizer ingredients function as a binder for theagglomerate as well as a nutrient source. To improve the mechanicalstrength, these preferred agglomerates may further comprise anadditional binder such as one of the lignosulfonate binders disclosedherein.

Depending on the calcium-containing secondary plant nutrient sourcesemployed, the particulate calcium source may contain appreciablequantities of CaO and may further contain other calcium-containingcompounds having the potential to react with water and form a solidhydrate, such as calcium sulfate (CaSO₄) and calcium sulfite (CaSO₃),which may be present in anhydrous or partially-hydrated forms. Othercompounds such as MgO and Na₂SO₄ will also hydrate, but are typicallypresent in relatively small proportions.

Cement kiln dust, for example, may contribute significantly to theconcentration of CaO and other calcium-containing compounds having thepotential to be hydrated present in the particulate calcium source. Thecomposition of cement kiln dust can vary significantly with thecomposition of the raw materials fed to the kiln, the kiln system, thefuel used to fire the kiln as well as the conditions encountered by thedust particles in the kiln and in the dust collection apparatus.Generally, cement kiln dust is comprised of varying amounts of elementssuch as Ca, Mg, Si, Al and Fe, trace amounts of heavy metals and adistribution of alkalies such as K, Na and Li. Most of these elementsare present as carbonates, sulfates, halides, hydroxides or oxides.Since the kiln dust has undergone some degree of calcination, the CaCO₃content in the dust is depleted relative to the kiln feed and asignificant portion of the calcium is instead present as CaO. Due to itscomposition which includes CaO, raw cement kiln dust exiting the kiln ishighly-reactive toward water and has the potential to hydrate and hardenif exposed to sufficient moisture.

A representative cement kiln dust composition is set forth in Table 1below. However, it should be understood that Table 1 is intended asmerely exemplary and cement kiln dust need not include all of theseconstituents in the concentrations listed below nor are other possibleconstituents excluded.

TABLE 1 Constituent % By Weight CaCO₃ 30-60 CaO  5-40 SiO₂ 10-20 Al₂O₃2-6 Fe₂O₃ 1-4 MgO 1-4 K₂SO₄ 3-9 CaSO₄ 2-8 Na₂SO₄ 1-3 KCl 1-3 KF 0.1-1  Heavy Metals trace

Like cement kiln dust, lime kiln dust and manure ash are finely dividedand contain high concentrations of calcium compounds, including CaO, andare similarly reactive toward water and have the potential to hydrateand harden when exposed to moisture. Although similar in composition tocement kiln dust, an even larger proportion of calcium present in limekiln dust is in the form of CaO. Lime kiln dust may contain 50% byweight or more CaO. Of course, the use of lime in the particulatecalcium source will also increase the CaO content.

When cement kiln dust, lime kiln dust, manure ash and lime are contactedwith water, CaO and other calcium-containing compounds present havinghydration potential react with the water and are hydrated. In the caseof CaO, the reaction product is Ca(OH)₂, whereas calcium sulfate reactswith water to form gypsum. The reaction of these components with wateris accompanied by a volumetric expansion or enlargement as they areconverted to their hydrate form. The hydration of CaO to Ca(OH)₂ lime isbelieved to be accompanied by a particularly significant volumetricexpansion. That is, it is believed that the potential of the particulatecalcium source used in the practice of the present invention, andultimately that of the preagglomerate mixture, to hydrate and expand ispredominantly attributable to the presence of CaO.

In the practice of the present invention, the preagglomerate mixturecomprising the various components of the product is agglomerated usingconventional tumble or growth agglomeration methods which includecontacting the mixture with water in a suitable agglomeration device.The volumetric expansion which accompanies the hydration of CaO andother calcium-containing compounds having the potential to be hydratedpresent in the preagglomerate may tend to reduce the mechanical strengthof the agglomerates if the concentration of these compounds in thepreagglomerate is excessive. In general, it has been discovered that ifthe combined concentration of CaO and other calcium-containing compoundshaving the potential to be hydrated in the preagglomerate exceeds about10% by weight (dry basis), the subsequent volumetric expansion of thesecomponents can significantly reduce the mechanical strength of theagglomerates. Therefore, the combined concentration of CaO and othercalcium-containing compounds having the potential to be hydrated in thepreagglomerate mixture is preferably no greater than about 10%, morepreferably no greater than about 7%, still more preferably no greaterthan about 5% and optimally no greater than about 3% by weight on a drybasis. Controlling the concentration of CaO and other calcium-containingcompounds having the potential to be hydrated in the preagglomeratemixture in this fashion advantageously minimizes the extent to which theresulting agglomerate will swell upon hydration so that an agglomerateexhibiting sufficient mechanical strength may be produced.

The concentration of CaO and other calcium-containing compounds havingthe potential to be hydrated in the preagglomerate mixture may becontrolled simply by limiting the amount of the sources of thesecompounds introduced into the preagglomerate. For example, if cementkiln dust containing about 30% by weight CaO is the only source of CaOand other calcium-containing compounds having the potential to behydrated in the particulate calcium source, the amount of cement kilndust introduced into the preagglomerate preferably does not exceed about33% by weight, more preferably does not exceed about 23% by weight,still more preferably does not exceed about 17% by weight and optimallydoes not exceed about 10% by weight of the preagglomerate mixture. Inaddition, limiting the proportion of cement kiln dust, lime kiln dustand/or manure ash in the preagglomerate may permit the use of suchmaterials containing relatively high concentrations of heavy metals(e.g., mercury, lead, arsenic etc.) or other potentially harmfulcomponents. That is, the balance of ingredients in the preagglomerateserve as a buffer to reduce the concentration of these components in theagglomerates so as to produce a suitable liming product that conformswith environmental guidelines.

Alternatively, the concentration of CaO and other calcium-containingcompounds having the potential to be hydrated in the preagglomeratemixture is controlled by prehydrating all or a portion of the componentsof the particulate calcium source containing such compounds. Forexample, upon contacting cement kiln dust with water, CaO, CaSO₄, CaSO₃and other components of the dust having hydration potential react withthe water and are hydrated, thereby reducing the hydration potential ofthe cement kiln dust and ultimately of the preagglomerate. Preferably,the material to be prehydrated is combined with an amount of water lessthan the stoichiometric amount necessary to totally hydrate thecomponents of the material in order to ease subsequent handling of thehydrated material in the agglomeration process. As the amount of watercombined with the material to be prehydrated approaches or exceeds thestoichiometric amount needed to totally hydrate the material, it becomesincreasingly difficult to form acceptable agglomerates because thehydrated material begins to cement together into progressively largerparticles which ultimately produce agglomerates that do not readilydisintegrate when exposed to water. By combining the material to beprehydrated with an amount of water less than the stoichiometric amountnecessary to totally hydrate the material, the partially-hydratedmaterial remains substantially dry and free-flowing and can be easilycombined with the other components of the preagglomerate.

In those applications where a component of the preagglomerate mixture isprehydrated, it may be advantageous to mix the material with wetted,gypsum-containing solids or slurry produced in lime scrubbing stackgases to remove sulfur dioxide. Lime scrubber solids typically containfrom about 15% to about 30% by weight water. The water present in thelime scrubber solids reacts with CaO and other calcium-containingcompounds having the potential to be hydrated in the material to beprehydrated and the solids further dilute the concentration of CaO andother calcium-containing compounds having the potential to be hydratedin the preagglomerate mixture. In addition to providing a convenient andeconomical source of prehydration water, including wetted lime scrubbersolids in the preagglomerate mixture is advantageous in thoseapplications where a sulfur-containing agglomerate is desired. Moreover,lime scrubber solids may provide a source of calcium, and gypsum inparticular, having a lower concentration of heavy metals thanparticulate calcium sources obtained from other sources and therebyserve as a more effective buffer in reducing the concentration of heavymetals or other potentially harmful components in the agglomerate.

As noted previously, the composition of cement kiln dust and othercomponents of the particulate calcium source containing CaO and othercalcium-containing compounds having the potential to be hydrated, aswell as the preagglomerate mixture can vary substantially. One way ofapproximating the concentration of CaO and other calcium-containingcompounds having the potential to be hydrated in cement kiln dust andother materials in the preagglomerate mixture is to first dry thematerial to constant weight at about 100° to about 120° C. The driedmaterial is then mixed with an amount of water in excess of the amountneeded to totally hydrate the material (e.g., an equivalent weight ofwater) and dried again to constant weight at about 100° to about 120° C.The concentration of CaO and other calcium-containing compounds havingthe potential to be hydrated in the material can then be approximatedfrom the difference between the weight of water added and the weight ofthe material after the second drying. This differential represents theamount of water reacted with CaO and other calcium-containing compoundshaving the potential to be hydrated present in the material to formhydrates and can be used to approximate the concentration of suchcompounds in the material and ultimately the preagglomerate mixture.

Alternatively, in the absence of a compositional analysis, a series ofagglomeration trials may be used to determine whether the concentrationof CaO and other calcium-containing compounds having the potential to behydrated in the preagglomerate mixture needs to be reduced, either bylimiting the amount of the source of these compounds introduced into thepreagglomerate or by prehydrating all or some of the particulate calciumsource and, if prehydration is employed, the amount of water required toadequately prehydrate the material. For example, it has been found thatthe amount of water necessary to achieve the proper extent ofpartial-hydration of cement kiln dust is usually between about 3% andabout 16% by weight, and more typically between about 4% and about 8% byweight based on the starting weight of cement kiln dust.

If components of the preagglomerate mixture are prehydrated, it ispreferred that substantially each particle of the material be uniformlycoated with water to assure greater compositional uniformity in theprehydrated material. This may be achieved by using a high energy pin,auger, paddle or ribbon type mixer capable of intimately mixing thematerial and water. In order to enhance the degree of contact betweenthe material to be prehydrated and the water and provide otherbeneficial effects, it is preferred to reduce the particle size of thematerial, if necessary, by ballmilling or other suitable means toachieve a particle size distribution as described below.

After the material to be prehydrated and water have been thoroughlymixed, the moistened material is preferably conditioned by storing itfor a time sufficient so that substantially all of the water is reactedwith the material. The moistened material discharged from the mixer maybe stored in a conditioning bin wherein the hydration reaction betweenthe water and the material is completed. In general, storage periods(i.e., conditioning times) from about 1 hour to as much as 24 hours arepreferred. The hydration reaction which occurs upon combining cementkiln dust and similar materials with water is highly exothermic and itsprogress is easily monitored as the moistened material is conditioned bymeasuring the temperature rise as the material reacts with the water.After conditioning, the partially-hydrated material is substantiallydry. Again, since the composition of cement kiln dust and othercomponents of the particulate calcium source may vary considerably, itmay be desirable to conduct a series of trials with a particularmaterial varying the storage time in order to ensure prehydration isaccomplished as desired.

Preferably, the particulate calcium source used to prepare theagglomerate is finely divided. More specifically, it is preferred thatparticulate calcium source comprise a mixture of particles having a sizedistribution of which less than about 1% by weight is +20 mesh and lessthan about 10% by weight is −20 +100 mesh. More preferably, less thanabout 20% by weight of the particles in the mixture is −100 +150 mesh.Still more preferably, at least about 50% by weight of the particles inthe mixture are −200 mesh. In a still more preferred embodiment, atleast about 75% by weight of the particles in the mixture are −200 meshand at least about 5%, at least about 25%, or even at least about 50% byweight are −325 mesh. In accordance with an especially preferredembodiment of the present invention, essentially all (e.g., at leastabout 95% by weight) of the particles in the particulate calcium sourceused to prepare the agglomerate are −100 mesh, preferably −150 mesh,more preferably −250 mesh and optimally −325 mesh. By using finelydivided calcium-containing particles in the agglomerate, conversion ofthe calcium to plant-usable form (i.e., ionic calcium) once theagglomerate is incorporated into soil is expedited and optimum calciumsaturation of the treated soil may be more readily attained.Finely-divided calcium-containing particles in the agglomerate areespecially advantageous in applications where the agglomerate contains aprimary plant nutrient source of the type typically used in N-P-Kfertilizer formulations. The finely divided calcium source is betterable to counteract the acidifying effect of the N-P-K fertilizercomponent, allowing more rapid transfer of nutrients to plants andreducing nutrient loss due to leaching. If necessary, ballmilling orother suitable means may be employed to obtain a desired particle sizedistribution in the particulate calcium source.

In order to provide agglomerates exhibiting a relatively uniformcomposition throughout and avoid segregation of the individualcomponents in the agglomerates, it is preferred that all of thematerials incorporated therein be similarly sized. However, theparticles of the various additives which may be present in theagglomerates may be somewhat larger than the particles of the calciumsource. Thus, for example, it is preferred that the mixture of all thevarious materials incorporated into the agglomerates have a particlesize distribution of which less than about 1% by weight is +20 mesh andless than about 15% by weight is −20 +100 mesh. More preferably, notmore than about 25% by weight of these particles is −100 +150 mesh.Still more preferably, at least about 20% by weight of the particles inthe mixture are −200 mesh. In a still more preferred embodiment, atleast about 50% by weight of the particles in the mixture are −200 meshand at least about 5%, at least about 25%, or even at least about 50%are −325 mesh. As with the calcium source, it may be necessary to reducethe particle size of the primary nutrient source and other additives byballmilling or other suitable means in order to obtain the desiredparticle size distribution.

The agglomerates of the present invention are prepared by pelletizing apreagglomerate mixture prepared by combining a water-soluble binder, theparticulate calcium source (some or all of which may have beenprehydrated) and, optionally, the other ingredients previouslymentioned. The materials combined in the preagglomerate are present inproportions sufficient to provide an agglomerate of the desiredcomposition. The preagglomerate may contain a portion of the waterrequired for pelletizing.

The water-soluble binder may be combined with the other components ofthe preagglomerate either as a solid or as an aqueous solution of thebinder. If an aqueous solution of a lignosulfonate salt is employed, thesolution suitably contains from about 48% to about 60% by weight solids.If a solid binder is used, it is preferred that a portion of the waternecessary for agglomeration of the preagglomerate (e.g., approximatelytwo-thirds) be added along with the binder to promote thorough mixing ofthe binder with the other components of the preagglomerate. It ispreferred that substantially each particle of the preagglomerate becoated with binder. This ensures uniformity in both the preagglomerateand in the final product and may be achieved by using a high energy pin,auger, paddle or ribbon type mixer capable of intimately mixing thecomponents of the preagglomerate.

Although in the preceding description the prehydration of theparticulate calcium source and addition of the binder were described astwo distinct steps, it should be understood that prehydration of thecalcium source and addition of the binder could take placesimultaneously in a single step. For example, the binder may be added tothe particulate calcium source as an aqueous solution of the binder, thebinder solution containing sufficient water to achieve the appropriatedegree of hydration of the calcium source. In such an operation, thecalcium source and binder solution could be combined in a high energymixture and then conditioned for a time sufficient to allowsubstantially all of the water to react with the calcium source. Aportion of the water necessary for pelletizing could then be added tothe conditioned material containing the binder along with any additivesto form the preagglomerate. Similarly, the particulate calcium source, asolid water-soluble binder and an appropriate amount of water could bemixed intimately in a high energy mixture, conditioned and mixed withadditional water and any additives to form a suitable preagglomerate.

The moistened preagglomerate mixture is fed directly to any suitableagglomeration device as is known in the art and pelletized to form theagglomerates. Once the agglomerates are formed, the binder and cementkiln dust particles form a matrix comprising the binder disposed withininterstices between dust particles which binds the agglomeratestogether. Suitable pelletizing devices include drum, tub and shallow pandisc pelletizers or any other suitable tumble or growth agglomerationdevice. Preferably, a shallow-pan disc pelletizer is employed as theagglomeration device. Once the degree of tilt and rotational speed ofthe pan are determined, pelletizing of the moistened preagglomerateproceeds as is well known to those skilled in the art. In addition tothese variables, more water is typically added in the pan to optimizethe size and consistency of the agglomerates produced on the shallow pandisc pelletizer. The various parameters of the pelletizing step arecontrolled as is known in the art so as to produce agglomerates having asize suitable for broadcast or row placement using conventionalfertilizer application equipment. Typically the agglomerates should be−3 +40 mesh, more preferably −6 +16 mesh.

After the agglomerates are discharged from the pelletizer, they aredried to remove a large portion of the internal water which is initiallypresent in the newly-formed agglomerates. Active drying of theagglomerates is preferred to obtain a product having the desiredmechanical strength and disintegration characteristics. If theagglomerates are not actively dried by heating, the water present in thefreshly pelletized agglomerates may continue to react with the remainingcomponents of the particulate calcium source which can still be hydratedand eventually form very hard, substantially non-disintegrableagglomerates resembling concrete. Preferably, the newly formedagglomerates are dried to reduce their moisture content to less thanabout 1% by weight, more preferably to less than about 0.5% by weight.

The agglomerates may be dried in any suitable apparatus. For example,drying may take place in an oven maintained at a temperature from about100° to about 140° C. or a vibrating fluidized bed dryer or rotary dryermay be employed. In a continuous process, vibrating fluidized bed orrotary dryers are preferred since migration of the binder towards theexterior of the agglomerate is reduced, providing a more uniform productexhibiting improved mechanical strength. If a vibrating fluidized beddryer is used, the dryer is suitably operated with a drying air entrancetemperature of about 315° C. and an exit air temperature of about 95° C.However, these temperatures may vary significantly with the residencetime of the agglomerates in the dryer. Preferably, the agglomerates donot exit the dryer at a temperature in excess of about 65° C. Dependingupon the additives incorporated into the agglomerate, the dryingtemperatures noted hereinabove may have to be decreased in order toavoid melting the agglomerate. Furthermore, once drying is complete, itis preferred to allow the agglomerates to cool before piling in order toavoid the agglomerates from clumping together.

Once dried, the agglomerates should have sufficient mechanical strengthto withstand normal handling, transportation and blending withoutfracturing and without excessive sloughing to form dust. There areseveral standardized methods that may be used for measuring mechanicalstrength of granular materials. However, a simple and widely-acceptedstandard is crush strength. Crush strength is measured by determiningthe minimum mass which crushes an agglomerate of particular size whenthe mass is placed on the agglomerate. In the practice of the presentinvention, the drying and removal of water from the newly-formedagglomerates is controlled such that dried agglomerates having a sizeranging from −7 to +8 mesh exhibit an average green crush strength of atleast about 2 pounds (about 0.9 kg), preferably at least about 4 pounds(about 1.8 kg), more preferably at least about 6 pounds (about 2.7 kg),still more preferably at least about 8 pounds (about 3.6 kg) andoptimally at least about 9 pounds (about 4.1 kg). By green crushstrength it is meant the crush strength of the dried agglomeratesimmediately after drying. In our experience, we have found that thenewly dried agglomerates continue to increase in hardness as they age.This may be due to residual moisture present in the dried agglomerateswhich continues to react with and hydrate components of the cement kilndust, resulting in further hardening of the agglomerate.

In order to inhibit dusting of the agglomerated product, a conventionaldust control agent may be employed. For example, a dust control agentsuch as that sold by Arr-Maz Products, Winter Haven, Fla. 33880, underthe product designation DUSTROL 30-52 may be spray applied to the heatedagglomerates exiting the dryer. Other additives may also be sprayapplied to the finished agglomerates. For example, if the agglomeratecontains a source of nitrogen, it may be advantageous to apply a coatingof a nitrogen volatilization inhibitor such as that commerciallyavailable from IMC Global, Bannockburn, Ill. 60015, under the trademark“AGRATAIN”. Alternatively, such a nitrogen volatilization inhibitorcould be incorporated into the preagglomerate mixture.

In certain states of the United States of America, liming agents such asthe agglomerates of the present invention must comply with localordinances which establish guidelines for the disintegrationcharacteristics of such agents when exposed to water. Generally, limingagents should disintegrate once incorporated in the soil and exposed towater (e.g., rain) so that the various beneficial components of theagent can be utilized by the soil. In addition to substantial mechanicalstrength, the agglomerates made in accordance with the present inventiondisintegrate rapidly when immersed in water. Once exposed to water, thewater-soluble binder in the agglomerates is readily dissolved, causingthe agglomerates to disintegrate into particles of substantially thesame size as the raw materials used to form the agglomerates, therebyallowing the agglomerates of the present invention to serve as afertilizer or an effective liming agent. In a preferred embodiment, theagglomerates of the present invention will dissolve in less than 10minutes, more preferably in less than 5 minutes, still more preferablyin less than 3 minutes, still more preferably in less than 2 minutes,and optimally in less than 1 minute when immersed in water at or nearroom temperature.

A process flow diagram is presented in the FIGURE illustrating anexample of the type of equipment and flow scheme which may be used inpracticing the present invention.

If prehydration of the particulate calcium source is employed, thecalcium source is loaded into bin 1 and discharged by feeder 2 at apredetermined rate into a high energy mixer 3 along with water from pump4 fed to the mixer at a rate sufficient to achieve the desired degree ofhydration. Suitable high energy mixing devices include the device shownin U.S. Pat. No. 4,881,887 (Holley) sold by Ferro-Tech, Inc., Wyandotte,Mich. 48192 under the trademark “FERRO-TECH-TURBULATOR”. Aftersufficient residence time in mixer 3 to ensure intimate contact betweenthe calcium source and the water, the hydrated mixture is dischargedfrom mixer 3 into conditioning bin 5 and stored for a period of timesufficient to ensure that substantially all of the water has reactedwith the particulate calcium source.

After conditioning, hydrated material is then discharged at apredetermined rate from bin 5 by feeder 6 into a second high energymixer 7 along with a water-soluble binder, either in a liquid or a solidform, fed to mixer 7 at a predetermined rate from storage bin 8.Alternatively, the water-soluble binder could be combined with theparticulate calcium source in mixer 3.

If prehydration of the cement kiln dust is not employed, it should beunderstood that bin 1, feeder 2 high energy mixer 3 and pump 4 areomitted from the process shown in the FIGURE and instead, theparticulate calcium source is loaded into bin 5.

Additional water for pelletizing from pump 9 may be added to mixer 7 asneeded to form the preagglomerate. If a product comprising theparticulate calcium source and binder with no other additives isdesired, then the preagglomerate issues from mixer 7 directly onto asuitable agitated agglomeration device 10 (e.g., a shallow pan discpelletizer). Preferably, the preagglomerate is pelletized using ashallow pan disc pelletizer of the type shown in U.S. Pat. Nos.4,726,755 (Holley) and 3,883,281 (Holley) sold by Ferro-Tech, Inc.,Wyandotte, Mich. 48192 under the trademark “FERRO-TECH”.

If primary plant nutrient source (e.g., potash, urea and other N-P-Kfertilizer components), other secondary plant nutrient source (e.g.,limestone) and/or a micronutrient source additive described hereinaboveare desired in the final agglomerates, these additives may be fed frombins 11 and 12 directly into mixer 7 along with the particulate calciumsource from feeder 6, binder from storage bin 8 and additional waterfrom pump 9 to form a suitable preagglomerate which is then fed toagglomeration device 10.

Agglomerates of the desired size discharged from the agglomerationdevice may then be fed directly into a suitable drying device (notshown) for drying.

The present invention is illustrated by the following examples which aremerely for the purpose of illustration and are not to be regarded aslimiting the scope of the invention or manner in which it may bepracticed. In the proceeding examples, reference to weight percentagesare based on the starting weight of cement kiln dust unless otherwisestated.

EXAMPLE 1

In this example, agglomerates were made from preagglomerate mixturescontaining varying amounts of CaO combined with CaCO₃, urea and/orpotash fines along with an aqueous solution of NORLIG A brand calciumlignosulfonate (about 54 weight percent lignosulfonate salt) as abinder. The preagglomerates were formed by thoroughly mixing CaO withmeasured quantities of CaCO₃, urea and/or potash fines. The CaO, CaCO₃,urea and potash fines each exhibited a particle size of −100 mesh. Onceformed, the preagglomerate was then hand fed to a shallow pan discpelletizer and formed into agglomerates. In some trials, the aqueoussolution of lignosulfonate binder was mixed with the other components ofthe preagglomerate before being introduced onto the pan, while in othertrials the binder was added to the other materials after they wereintroduced onto the pan. It is preferred that the binder be thoroughlyincorporated into the preagglomerate mixture prior to being introducedinto the pan. During pelletizing, approximately 5 to 8 weight percent ofadditional water (based on the weight of the preagglomerate includingthe lignosulfonate binder) was sprayed onto the agglomerates as theyformed in the pan. The agglomerates were removed from the pan by handand dried in an oven at 60-85° C. for approximately 30 minutes. Afterdrying, the resulting agglomerates were screened to produce agglomerateshaving a size ranging from approximately −6 to +16 mesh. If possible,the green crush strength of the dried, screened agglomerates wasdetermined. Set forth in Table 2 below is the composition of thepreagglomerates and the observed results.

TABLE 2 Preagglomerate Composition (wt %) Results CaO Potash CaCO₃ UreaBinder Crush Strength (lb) 95  — — — 5 fell apart 50  — 45 — 5 fellapart 25  — 70 — 5 fell apart 10  — 85 — 5 fell apart 7 — 88 — 5 4.3 5 —90 — 5 6.4 3 — 92 — 5 9.0 5 — 88 — 7 7.0 7 — 86 — 7 4.2 10  — 81 — 9 −250  — — 45 5 fell apart 25  — — 70 5 fell apart 10  — — 85 5 3.0 7 — —88 5 5.8 5 — — 90 5 8.2 3 — — 92 5 9.6 10  — — 83 7 6.0 7 — — 86 7 7.1 5— — 88 7 8.1 50  45 — — 5 fell apart 25  70 — — 5 fell apart 10  85 — —5 3.2 7 88 — — 5 5.9 5 90 — — 5 8.0 3 92 — — 5 9.2 10  83 — — 7 5.3 7 86— — 7 6.9 5 88 — — 7 8.0 50  22.5 — 22.5 5 fell apart 25  35 — 35 5 fellapart 10  42.5 — 42.5 5 3.2 7 44 — 44 5 6.0 5 45 — 45 5 7.9 3 46 — 46 58.4

EXAMPLE 2

Three samples of cement kiln dust taken directly from the dustcollection apparatus of a portland cement plant (Plant A) were hydratedusing varying amounts of water. The three samples were combined in ahigh energy mixer with 10, 14 and 16 weight percent water, respectivelyand stored in sealed containers for approximately 24 hours. Each sampleof hydrated material was then mixed with 7 weight percent potash, 5weight percent of an aqueous solution of NORLIG A brand calciumlignosulfonate (about 54 weight percent lignosulfonate salt) andadditional water in a high energy mixer to form a preagglomerate. Thepreagglomerate was then fed to a FERRO-TECH brand shallow pan discpelletizer and formed into agglomerates. During pelletizing,approximately 5 weight percent of additional water was added to theforming agglomerates. The agglomerates had a size ranging fromapproximately −6 to +16 mesh. These agglomerates were then oven dried at120° C. for approximately 24 hours. The dried agglomerates from allthree runs exhibited a green crush strength of approximately 3 pounds(about 1.4 kg) and disintegrated in a matter of minutes when immersed inwater.

EXAMPLE 3

Four samples of cement kiln dust were taken directly from the dustcollection apparatus of each of two other portland cement plants (PlantsC and L) and hydrated using varying amounts of water. The four samplesfrom each plant were combined in a high energy mixture with 4, 6, 8 and10 weight percent water, respectively, and stored in sealed containersfor approximately 24 hours. Each of the samples of hydrated material wasthen mixed with 8 weight percent of an aqueous solution of NORLIG Abrand calcium lignosulfonate (about 54 weight percent lignosulfonatesalt) and additional water in a high energy mixer to produce apreagglomerate. The preagglomerate was then fed to a FERRO-TECH brandshallow pan disc pelletizer and formed into agglomerates. Duringpelletizing, approximately 2.5 to 5 weight percent of additional waterwas added to the forming agglomerates. The agglomerates had a sizeranging from approximately −6 to +16 mesh. These agglomerates were thenoven dried at 120° C. for approximately 24 hours. The dried agglomeratesfrom all eight runs exhibited a green crush strength of approximately 1to 3 pounds (about 0.5 to 1.4 kg). The crush strength was found toincrease as the amount of water used to partially hydrate the dust wasincreased. However, the agglomerates made from the dust hydrated with 4weight percent water disintegrated in 1 to 2 minutes when immersed inwater, while the agglomerates made from the dust hydrated with 10 weightpercent water disintegrated in 10 to 20 minutes. The disintegration rateof agglomerates made from the dust samples hydrated with 6 and 8 weightpercent water fell between these two values.

EXAMPLE 4

Four samples of cement kiln dust taken directly from the dust collectionapparatus of Plant C were processed exactly as described in Example 3except that (1) in addition to the aqueous solution of NORLIG A brandcalcium lignosulfonate, 8 weight percent of potash was added to thehydrated material; and (2) instead of approximately 2.5 to 5 weightpercent, approximately 10 weight percent of additional water was addedto the forming agglomerates during pelletizing. Similar results to thosein Example 3 were achieved. The dried agglomerates from all four runsexhibited a green crush strength of approximately 1 to 3 pounds (about0.5 to 1.4 kg) which tended to increase as the amount of water used topartially hydrate the dust was increased. Similarly, the disintegrationrate of the agglomerates decreased as the amount of water used topartially hydrate the dust was increased.

The data from Example 3 and the present example demonstrate the effectof varying the amount of water used to hydrate the dust on the rate ofdisintegration of the final agglomerate. Thus, by varying the amount ofwater used to hydrate a particular dust, the disintegrationcharacteristics of the agglomerate may be altered as desired. Thus, inExample 3 and the present example, if a high rate of disintegration isdesired, then the agglomerates made using 4 weight percent water wouldbe preferred.

The agglomerates made in the present example were subjected to a wetsieving test to better examine the disintegration characteristics ofthese pellets. The wet sieving test was conducted by stacking fivesieves of differing mesh size such that the sieve opening decreasedprogressively from the top sieve to the bottom sieve. After weighing, asample of the agglomerates made in the present example was immersed inwater for approximately 48 hours. The moistened material was thendeposited on the top sieve and subjected to a gentle spray of washwater. As the material disintegrated, it passed through the top sievealong with the wash water and was deposited onto the next sieve. Washwater was applied to the top sieve until the water draining through thesieve was substantially clear. The top sieve was then removed and thewashing process repeated on each subsequent sieve in the stack in thesame fashion as described above. Each of the sieves and any materialremaining on the screens were heated to remove substantially all themoisture and then weighed. The weight of material (dry) which did notpass through each sieve was determined by subtracting the tare weight ofeach sieve. Summarized in Table 3 below is the weight percentage ofmaterial (based on the starting weight of the sample of agglomerates)which did not pass through each of the five sieves in the wet screeningtest.

TABLE 3 Tyler Standard Weight % Sieve Sieve Series Not Passing Top 9 0Second 20 0 Third 32 0 Fourth 60 0.8 Bottom 100 7.0

As noted in Table 3, the agglomerates subjected to the wet screeningtest disintegrated such that all of the resulting particulate matter hada nominal diameter less than 500 μm (i.e., −32 mesh) and substantiallyall of the resulting particles had a nominal diameter less than 150 μm(i.e., −100 mesh).

EXAMPLE 5

A sample of cement kiln dust taken directly from the dust collectionapparatus of Plant A was processed exactly as described in Example 2using 10 weight percent water to hydrate the dust and using only potash(7 weight percent) as the binder. After oven drying, the resultingagglomerates having a size ranging from approximately −6 to +16 meshexhibited a green crush strength of approximately 3 pounds (about 1.4kg) and disintegrated in a matter of minutes when immersed in water.

EXAMPLE 6

A sample of cement kiln dust taken directly from the dust collectionapparatus of Plant A was processed exactly as described in Example 2using 14 weight percent water to hydrate the dust and using only 7weight percent of an aqueous solution of NORLIG A brand calciumlignosulfonate (about 54 weight percent lignosulfonate salt) as thebinder. A slightly larger amount of the lignosulfonate salt solution wasused than in Example 2 to compensate for the loss of binding action dueto the absence of potash. After oven drying, the resulting agglomerateshaving a size ranging from approximately −6 to +16 mesh exhibited agreen crush strength ranging from approximately 2 to 3 pounds (about 1to 1.4 kg) and disintegrated in a matter of minutes when immersed inwater.

EXAMPLE 7

A sample of cement kiln dust taken directly from the dust collectionapparatus of Plant A was processed exactly as described in Example 2except that the dust was not hydrated before adding the binder. Afteroven drying, the resulting agglomerates having a size ranging fromapproximately −6 to +16 mesh exhibited essentially no crush strength,falling apart by simple vibration or touch of the hand.

This example demonstrates the importance of controlling theconcentration of CaO and other calcium-containing compounds having thepotential to be hydrated in the preagglomerate. Unless the cement kilndust is sufficiently hydrated before pelletizing or combined withmaterials in the preagglomerate to sufficiently dilute the hydrationpotential, the components of the preagglomerate will tend to hydrateexcessively during formation of the agglomerate. Such hydration isaccompanied by a volumetric expansion of the formed agglomerate whichrenders the agglomerate weak and undesirable for agricultural uses.

EXAMPLE 8

A sample of cement kiln dust taken directly from the dust collectionapparatus of Plant C was combined in a high energy mixture with 14weight percent water using a residence time of approximately 1 hour. Thehydrated material was then mixed with both 7 weight percent potash and 5weight percent of an aqueous solution of NORLIG A brand calciumlignosulfonate (about 54 weight percent lignosulfonate salt) in a highenergy mixer to form a preagglomerate. The preagglomerate was then fedto a FERRO-TECH brand shallow pan disc pelletizer to form agglomerates.During pelletizing, approximately 2.5 weight percent of additional waterwas added to the forming agglomerates. The agglomerates formed had asize ranging from approximately −6 to +16 mesh. These agglomerates werethen oven dried at 120° C. for approximately 24 hours. The driedagglomerates exhibited a green crush strength of from approximately 1 to2 pounds (about 0.5 to 0.9 kg) and disintegrated in 10 to 20 minuteswhen immersed in water.

It is believed that the somewhat lower crush strength of theagglomerates produced in this example as compared to Example 2 is aresult of the cement kiln dust containing lower concentrations of CaOand other components which hydrate upon exposure to water as compared tothe dust used in Example 2. Therefore, the amount of hydration watershould be reduced.

EXAMPLE 9

A sample of cement kiln dust from Plant C was removed from an outdoordisposal site where it had been exposed to atmospheric moisture and rainand was presumably completely hydrated. This sample was formed intoagglomerates without further hydration and without using a binder.During pelletizing, approximately 5 weight percent of additional waterwas added to the forming agglomerates. The agglomerates formed had asize ranging from approximately −6 to +16 mesh. These agglomerates werethen oven dried at 120° C. for approximately 24 hours. The driedagglomerates exhibited a green crush strength of approximately 6 pounds(about 2.7 kg) but did not disintegrate after several months ofimmersion in water and, thus, would not be suitable for agriculturaluses.

This example demonstrates the importance of adding a water-solublebinder in producing an agglomerate having desirable disintegrationcharacteristics.

EXAMPLE 10

A 2.3 kg sample of cement kiln dust taken directly from the dustcollection apparatus of Plant C was ballmilled to a bulk density ofabout 863 kg/m³. The ballmilled dust was hydrated by combining it with 8weight percent (0.18 kg) water in a high energy mixer. After two minutesof mixing, the material was removed from the mixer and transferred intoa sealed container. In order to simulate bin storage of a large quantityof hydrating cement kiln dust, the sealed container was placed in anoven maintained at about 65° C. for a period of about 24 hours.Approximately 1 kg of the hydrated dust was then mixed with about 1 kgof ballmilled urea and approximately 0.16 kg of an aqueous solution ofNORLIG A brand calcium lignosulfonate (about 54 weight percentlignosulfonate salt) in a high energy mixer for approximately 18seconds. This mixture was then fed to a FERRO-TECH brand shallow pandisc pelletizer and formed into agglomerates. Approximately 7.5 weightpercent of water (based on combined weight of hydrated dust and urea)was added to the mixture in the form of solvent in the aqueous bindersolution and as pelletizing water in the pan. The formed agglomerateswere removed from the pan, allowed to stand at room temperature forabout 24 hours and dried in a portable fluidized bed dryer at 38° to 50°C. for approximately 15 minutes. The dried agglomerates were sievedscreened to a size ranging from −6 to +16 mesh. Agglomerates ranging insize from −7 to +8 mesh exhibited a green crush strength of about 8pounds (about 3.6 kg) and a bulk density of about 855 kg/m³.

The dried agglomerates were analyzed for both total calcium and totalnitrogen content using comprehensive analysis methods. Total calciumcontent was determined by digesting a sample of pulverized agglomeratesin HCl over heat, diluting the resulting solution and subjecting it toatomic absorption analysis. Total nitrogen content was determined inaccordance with Association of Official Analytical Chemist (AOAC) MethodNo. 2.059. The agglomerates contained 14.85 weight percent calcium and19.40 weight percent nitrogen. For purposes of comparative limingcapacity, the Ca content of the agglomerates in this example correspondsto 20.78 weight percent as CaO and 37.11 weight percent as CaCO₃.

EXAMPLE 11

A 2.3 kg sample of cement kiln dust taken directly from the dustcollection apparatus of Plant L was ballmilled to a bulk density ofabout 679 kg/m³. The ballmilled dust was hydrated by combining it with 8weight percent (0.18 kg) water in a high energy mixer. After two minutesof mixing, the material was removed from the mixer and transferred intoa sealed container. In order to simulate bin storage of a large quantityof hydrating cement kiln dust, the sealed container was placed in anoven maintained at about 65° C. for a period of about 24 hours.Approximately 1 kg of the hydrated dust was then mixed with about 1 kgof ballmilled urea and approximately 0.16 kg of an aqueous solution ofNORLIG A brand calcium lignosulfonate (about 54 weight percentlignosulfonate salt) in a high energy mixer for approximately 18seconds. This mixture was then fed to a FERRO-TECH brand shallow pandisc pelletizer and formed into agglomerates. Approximately 9.5 weightpercent of water (based on combined weight of hydrated dust and urea)was added to the mixture in the form of solvent in the aqueous bindersolution and as pelletizing water in the pan. The formed agglomerateswere removed from the pan, allowed to stand at room temperature forabout 24 hours and dried in a portable fluidized bed dryer at 38° to 50°C. for approximately 15 minutes. The dried agglomerates were sievedscreened to a size ranging from −6 to +16 mesh. Agglomerates ranging insize from −7 to +8 mesh exhibited a green crush strength of about 8pounds (about 3.6 kg) and a bulk density of about 714 kg/m³.

The dried agglomerates were analyzed for both total calcium and totalnitrogen content using the same methods as described in Example 10. Theagglomerates contained 14.19 weight percent calcium and 19.50 weightpercent nitrogen. For purposes of comparative liming capacity, the Cacontent of the agglomerates in this example corresponds to 19.86 weightpercent as CaO and 35.47 weight percent as CaCO₃.

EXAMPLE 12

A 2.3 kg sample of cement kiln dust taken directly from the dustcollection apparatus of Plant C was ballmilled to a bulk density ofabout 863 kg/m³. The ballmilled dust was hydrated by combining it with 8weight percent (0.18 kg) water in a high energy mixer. After two minutesof mixing, the material was removed from the mixer and transferred intoa sealed container. In order to simulate bin storage of a large quantityof hydrating cement kiln dust, the sealed container was placed in anoven maintained at about 65° C. for a period of about 24 hours.Approximately 1.5 kg of the hydrated dust was then mixed with about 0.5kg of particulate dolomitic limestone, approximately 0.16 kg of anaqueous solution of NORLIG A brand calcium lignosulfonate (about 54weight percent lignosulfonate salt) and 75 ml of water in a high energymixer for approximately 18 seconds. This mixture was then fed to aFERRO-TECH brand shallow pan disc pelletizer and formed intoagglomerates. Approximately 18 weight percent of water (based oncombined weight of hydrated dust and dolomitic limestone) was added tothe mixture in the form of solvent in the aqueous binder solution and aspelletizing water in the pan. After being removed from the pan, a sampleof the agglomerates were dried immediately in a portable fluidized beddryer at 38° to 50° C. for approximately 15 minutes, while the remainderof the agglomerates were allowed to first stand at room temperature forabout 24 hours and then dried in the portable fluidized bed dryer. Thedried agglomerates were sieved screened to a size ranging from −6 to +16mesh. The agglomerates which were allowed to stand 24 hours and having asize ranging from −7 to +8 mesh exhibited a green crush strength ofabout 2.4 pounds (about 1.1 kg) and a bulk density of about 1057 kg/m³,while similarly sized agglomerates which were dried immediately in thefluidized bed dryer exhibited green crush strengths between about 2 andabout 3 pounds (between about 1 and about 1.4 kg). If desired, the greencrush strength of the agglomerates could be increased by using a largerquantity of binder.

EXAMPLE 13

Urea (2.4 pounds), crushed limestone (0.8 pounds), and non-prehydratedcement kiln dust (0.8 pounds) were mixed with water (Test 13-1) or abinder (a solution of lignosulfonate having approximately 50%solids—Test 13-2) in a Model 12TB34 Batch Turbulator for 18 seconds toform preagglomerates. The preagglomerates were hand fed to a Model 024″2′0″ Disc Pelletizer in which water was being sprayed onto the disc at a4:30/6:30 positions. The agglomerates were removed by hand and dried at120° F. to produce screened dry pellets (−6 +16 mesh). The moisturecontent and bulk density of the starting materials are presented belowin Table 4:

TABLE 4 Raw Data Moisture Bulk Density Urea N/A 636 kg/m₃ Limestone 0%1330 kg/m₃ Cement Kiln Dust 0% 867 kg/m₃

The resulting agglomerates were analyzed and found to have the followingcharacteristics:

TEST 13-1 Binder (water only) Amount of water at Patch Turbulator 50 mlMoisture from disc. 7% Product bulk density 764 kg/m³ Crush Strengthaverage (−6 +8 mesh) 6 pounds (2.7 kg)

TEST 13-2 Binder 3% Lignin Amount of Water at Batch Turbulator 50 mlMoisture from Disc. 7% Product Bulk Density 772 kg/m³ Crush StrengthAveraqe (−6 +8 mesh) 7 pounds (3.2 kg)

EXAMPLE 14

The procedure of Example 13 was repeated except that urea (2.4 pounds)and cement kiln dust (1.6 pounds) were mixed with 50 ml water in theBatch Turbulator for 18 seconds. The results were as follows:

Moisture from Disc 7%

Product Bulk Density 706 kg/m³

Crush Strength Average (−6 +8 mesh) 3 pounds (1.4 kg)

EXAMPLE 15

In this example, agglomerates were made from preagglomerate mixturescontaining varying amounts of lime kiln dust, manure ash and potashfines along with KGA-300 liquid wood waste derivative as a binder. Thelime kiln dust and manure ash were analyzed and determined to containabout 55% and about 7% by weight CaO, respectively. The lime kiln dustand manure ash exhibited a particle size distribution such that 90% ofthe particles were −300 mesh. The potash fines exhibited a particle sizedistribution such that 90% of the particles were −150 mesh.

The preagglomerate mixtures were formed by thoroughly mixing measuredquantities of lime kiln dust, manure ash and potash fines with theliquid binder. The preagglomerate was hand fed to a shallow pan discpelletizer and formed into agglomerates. In some trials, the liquid woodwaste binder was mixed with the other components of the preagglomeratebefore being introduced onto the pan, while in other trials the binderwas sprayed onto the other materials after they were introduced onto thepan. In order to render the liquid binder better suited for sprayapplication, the binder was heated to about 80° C. It is preferred thatthe binder be thoroughly incorporated into the preagglomerate mixtureprior to being introduced into the pan. During pelletizing,approximately 5 to 8 weight percent of additional water (based on theweight of the preagglomerate including the liquid binder) was sprayedonto the agglomerates as they formed in the pan. The agglomerates wereremoved from the pan by hand and dried in an oven at 60-85° C. forapproximately 30 minutes. After drying, the resulting agglomerates werescreened to produce agglomerates having a size ranging fromapproximately −6 to +16 mesh. If possible, the green crush strength ofthe dried, screened agglomerates was determined. Set forth in Table 5below is the composition of the preagglomerates and the observedresults.

TABLE 5 Preagglomerate Composition (wt %) Lime Kiln Manure Results DustAsh Potash Binder Crush Strength (lb) 55 — 45 5 fell apart 25 — 70 5fell apart 10 — 87 3 4.0 10 43.5 43.5 3 5.5 — 95 — 5 5.0

EXAMPLE 16

In this example, agglomerates were made from preagglomerate mixturescontaining varying amounts of a mixture of lime kiln dust and wettedgypsum combined with potash fines along with KGA-300 liquid wood wastederivative as a binder. The lime kiln dust was analyzed and determinedto contain about 55% by weight CaO. The lime kiln dust exhibited aparticle size distribution such that 90% of the particles were −300mesh. The potash fines exhibited a particle size distribution such that90% of the particles were −150 mesh. The wetted gypsum was obtained froma lime scrubbing unit used to remove sulfur dioxide from the gaseouseffluent of an electric power plant and was about 98% pure with a watercontent of about 22% by weight.

The lime kiln dust and wetted gypsum were combined in a weightproportion of 2 to 3 and mixed thoroughly. The resulting mixture wasthen allowed to set for approximately 12 hours, allowing water presentin the wetted gypsum to react with the lime kiln dust. Afterconditioning in this fashion, the lime kiln dust/gypsum mixture appearedessentially dry to the touch. The preagglomerate mixtures were formed bythoroughly mixing measured quantities of the conditioned lime kilndust/gypsum mixture, potash fines and the liquid binder. Thepreagglomerate was hand fed to a shallow pan disc pelletizer and formedinto agglomerates. In order to render the liquid binder better suitedfor spray application, the binder was heated to about 80° C. Duringpelletizing, approximately 5 to 8 weight percent of additional water(based on the weight of the preagglomerate including the liquid binder)was sprayed onto the agglomerates as they formed in the pan. Theagglomerates were removed from the pan by hand and dried in an oven at60-85° C. for approximately 30 minutes. After drying, the resultingagglomerates were screened to produce agglomerates having a size rangingfrom approximately −6 to +16 mesh. If possible, the green crush strengthof the dried, screened agglomerates was determined. Set forth in Table 6below is the composition of the preagglomerates and the observedresults.

TABLE 6 Preagglomerate (wt %) Lime Kiln Dust/ Results Wetted GypsumPotash Binder Crush Strength (lb) 50 45 5 3.5 30 65 5 6.0

In view of the above, it will be seen that the several objects of theinvention are achieved.

As various changes could be made in the above-described inventionwithout departing from the scope of the invention, it is intended thatall matter contained in the above description be interpreted asillustrative and not in a limiting sense.

What is claimed is:
 1. A process for forming an agglomerate for use as asoil conditioning agent, the process comprising: preparing apreagglomerate containing a water-soluble binder and a particulatecalcium source comprising CaO or Ca(OH)₂, the combined concentration ofCaO and other calcium-containing compounds having the potential to behydrated in the preagglomerate being no greater than about 10% byweight; pelletizing the preagglomerate to form the agglomerate, theproportion of the particulate calcium source in the preagglomerate beingsufficient such that the agglomerate contains at least about 15% byweight of the particulate calcium source; and drying the agglomerate,the drying being controlled such that dried agglomerates having a sizeranging from −7 to +8 Tyler Standard Sieve Series exhibit an averagegreen crush strength of at least about 2 pounds.
 2. The process as setfort in claim 1 wherein the concentration of CaO and othercalcium-containing compounds having the potential to be hydrated in thepreagglomerate is not greater than about 7% by weight.
 3. The process asset fort in claim 2 wherein the concentration of CaO and othercalcium-containing compounds having the potential to be hydrated in thepreagglomerate is not greater than about 5% by weight.
 4. The process asset fort in claim 3 wherein the concentration of CaO and othercalcium-containing compounds having the potential to be hydrated in thepreagglomerate is not greater than about 3% by weight.
 5. The process asset forth in claim 1 wherein the preagglomerate comprises at least about1% by weight of the water-soluble binder.
 6. The process as set forth inclaim 5 wherein the water-soluble binder comprises one or more materialsselected from the group consisting of lignosulfonates, lignosulfonatesalts, potash, urea, ammonium nitrate, diammonium phosphate, polyvinylalcohol, polyacrylic acid salts, amylose, methylcellulose,hydroxyethylcellulose, carboxymethylcellulose,ethylhydroxyethylcellulose, corn starch, wheat starch and sugar-basedbinders.
 7. The process as set forth in claim 6 wherein thewater-soluble binder comprises an aqueous solution of a lignosulfonatesalt.
 8. The process as set forth in claim 1 wherein the particulatecalcium source comprises a material selected from the group consistingof cement kiln dust, lime kiln dust, manure ash and mixtures thereof. 9.The process as set forth in claim 8 wherein the particulate calciumsource consists essentially of cement kiln dust.
 10. The process as setforth in claim 8 wherein the particulate calcium source furthercomprises at least one other calcium-containing secondary plant nutrientsource selected from the group consisting of limestone, dolomiticlimestone, gypsum, lime, hydrated lime and mixtures thereof.
 11. Theprocess as set forth in claim 10 wherein the at least one othercalcium-containing secondary plant nutrient source constitutes no morethan about 80% by weight of the particulate calcium source.
 12. Theprocess as set forth in claim 11 wherein the particulate calcium sourcehas a particle size distribution such that at least about 95% by weightof the particulate calcium source is −100 mesh Tyler Standard SieveSeries.
 13. The process as set forth in claim 10 wherein thepreagglomerate further comprises a primary plant nutrient sourceselected from the group consisting of ammonium nitrate, ammoniumsulfate, alkali metal nitrates, urea, rock phosphate, ammoniumphosphate, bone meal slag, aluminum phosphate, superphosphate, potash,potassium salts and mixtures thereof.
 14. The process as set forth inclaim 1 wherein at least a portion of the particulate calcium source inthe preagglomerate is prehydrated by combining the calcium source withan amount of water less than the stoichiometric amount necessary tototally hydrate the calcium source to produce partially-hydratedparticulate calcium source.
 15. The process as set forth in claim 14wherein the preagglomerate is formed by first combining at least aportion of the particulate calcium source with an amount of water lessthan the stoichiometric amount necessary to totally hydrate the calciumsource to produce partially-hydrated particulate calcium source and thencombining the partially-hydrated particulate calcium source with thewater-soluble binder.
 16. The process as set forth in claim 14 whereinthe reaction between the particulate calcium source and water to formthe partially-hydrated particulate calcium source is carried out byintimately mixing the calcium source and the water and storing themixture for a period of time sufficient so that substantially all of thewater is reacted with the calcium source.
 17. The process as set forthin claim 1 wherein the drying of the agglomerates is controlled suchthat dried agglomerates having a size ranging from −7 to +8 TylerStandard Sieve Series exhibit an average green crush strength of atleast about 4 pounds.
 18. An agglomerate for use as a soil conditioner,the agglomerate being formed by pelletizing a preagglomerate containinga water-soluble binder, a primary plant nutrient source providing asource of available nitrogen and a particulate calcium source comprisingCaO or Ca(OH)₂, the proportions of the primary plant nutrient source andthe particulate calcium source in the preagglomerate being sufficientsuch that the agglomerate comprises about 15% to about 60% by weight ofthe particulate calcium source and about 30% to about 80% by weight ofthe primary plant nutrient source, the combined concentration of CaO andother calcium-containing compounds having the potential to be hydratedin the preagglomerate being no greater than about 10% by weight, theagglomerate having a size ranging from −7 to +8 Tyler Standard SieveSeries exhibiting an average green crush strength of at least about 2pounds.
 19. The agglomerate as set forth in claim 18 wherein the primaryplant nutrient source is selected from the group consisting of urea,ammonium nitrate, ammonium sulfate, alkali metal nitrates, ammoniumphosphate, bone meal slag and mixtures thereof.
 20. An agglomerate foruse as a soil conditioner, the agglomerate being formed by pelletizing apreagglomerate containing a water-soluble binder, a primary plantnutrient source providing a source of potassium and a particulatecalcium source comprising CaO or Ca(OH)₂, the proportions of the primaryplant nutrient source and the particulate calcium source in thepreagglomerate being sufficient such that the agglomerate comprisesabout 15% to about 60% by weight of the particulate calcium source andabout 30% to about 80% by weight of the primary plant nutrient source,the combined concentration of CaO and other calcium-containing compoundshaving the potential to be hydrated in the preagglomerate being nogreater than about 10% by weight, the agglomerate having a size rangingfrom −7 to +8 Tyler Standard Sieve Series exhibiting an average greencrush strength of at least about 2 pounds.
 21. The agglomerate as setforth in claim 20 wherein the primary plant nutrient source is selectedfrom the group consisting of potash, potassium salts and mixturesthereof.
 22. A process for forming an agglomerate for use as a soilconditioning agent, the process comprising: preparing a preagglomeratecontaining a water-soluble binder and a particulate calcium sourcecomprising CaO or Ca(OH)₂ combined with at least one othercalcium-containing secondary plant nutrient source selected from thegroup consisting of limestone, dolomitic limestone, gypsum, lime,hydrated lime and mixtures thereof, the particulate calcium sourcehaving a particle size distribution such that less than about 1% byweight of the particulate calcium source is +20 mesh and less than about10% by weight of the particulate calcium source is −20 +100 mesh TylerStandard Sieve Series, the combined concentration of CaO and othercalcium-containing compounds having the potential to be hydrated in thepreagglomerate being no greater than about 10% by weight; pelletizingthe preagglomerate to form the agglomerate; and drying the agglomerate,the drying being controlled such that dried agglomerates having a sizeranging from −7 to +8 Tyler Standard Sieve Series exhibit an averagegreen crush strength of at least about 2 pounds.
 23. The process as setforth in claim 22 wherein the particulate calcium source has a particlesize distribution such that less than about 20% by weight of theparticulate calcium source is −100 +150 mesh Tyler Standard SieveSeries.
 24. The process as set forth in claim 23 wherein the particulatecalcium source has a particle size distribution such that at least about50% by weight of the particulate calcium source is −200 mesh TylerStardard Sieve Series.
 25. The process as set forth in claim 24 whereinthe particulate calcium source has a particle size distribution suchthat at least about 75% by weight of the particulate calcium source is−200 mesh and at least about 5% by weight of the particulate calciumsource is −325 mesh Tyler Standard Sieve Series.
 26. The process as setforth in claim 22 wherein the particulate calcium source has a particlesize distribution such that at least about 95% by weight of theparticulate calcium source is −100 mesh Tyler Standard Sieve Series. 27.The process as set forth in claim 26 wherein the particulate calciumsource has a particle size distribution such that at least about 95% byweight of the particulate calcium source is −150 mesh Tyler StandardSieve Series.
 28. The process as set forth in claim 27 wherein theparticulate calcium source has a particle size distribution such that atleast about 95% by weight of the particulate calcium source is −250 meshTyler Standard Sieve Series.
 29. The process as set forth in claim 28wherein the particulate calcium source has a particle size distributionsuch that at least about 95% a by weight of the particulate calciumsource is −325 mesh Tyler Standard Sieve Series.
 30. An agglomerate foruse as a soil conditioner, the agglomerate being formed by pelletizing apreagglomerate containing a water-soluble binder and a particulatecalcium source comprising CaO or Ca(OH)₂ combined with at least oneother calcium-containing secondary plant nutrient source selected fromthe group consisting of limestone, dolomitic limestone, gypsum, lime,hydrated lime and mixtures thereof, the particulate calcium sourcehaving a particle size distribution such that less than about 1% byweight of the particulate calcium source is +20 mesh and less than about10% by weight of the particulate calcium source is −20 +100 mesh TylerStandard Sieve Series, the combined concentration of CaO and othercalcium-containing compounds having the potential to be hydrated in thepreagglomerate being no greater than about 10% by weight.
 31. Theagglomerate as set forth in claim 30 wherein the particulate calciumsource has a particle size distribution such that less than about 20% byweight of the particulate calcium source is −100 +150 mesh TylerStandard Sieve Series.
 32. The agglomerate as set forth in claim 31wherein the particulate calcium source has a particle size distributionsuch that at least about 50% by weight of the particulate calcium sourceis −200 mesh Tyler Standard Sieve Series.
 33. The agglomerate as setforth in claim 32 wherein the particulate calcium source has a particlesize distribution such that at least about 75% by weight of theparticulate calcium source is −200 mesh and at least about 5% by weightof the particulate calcium source is −325 mesh Tyler Standard SieveSeries.
 34. The agglomerate as set forth in claim 30 wherein theparticulate calcium source has a particle size distribution such that atleast about 95% by weight of the particulate calcium source is −100 meshTyler Standard Sieve Series.
 35. The agglomerate as set forth in claim34 wherein the particulate calcium source has a particle sizedistribution such that at leant about 95% by weight of the particulatecalcium source is −150 mesh Tyler Standard Sieve Series.
 36. Theagglomerate as set forth in claim 35 wherein the particulate calciumsource has a particle size distribution such that at least about 95% byweight of the particulate calcium source is −250 mesh Tyler StandardSieve Series.
 37. The agglomerate as set forth in claim 36 wherein theparticulate calcium source has a particle size distribution such that atleast about 95% by weight of the particulate calcium source is −325 meshTyler Standard Sieve Series.